The present invention relates to light sampling devices for producing a sample of light from an optical device, e.g., for control or other processing purposes. The invention is especially useful in an image projector system including a plurality of image projectors, wherein the light samples produced by each projector are used for controlling the image projectors, e.g., to compensate for variations in color composition, light intensity, etc. The invention is therefore described below with respect to this application, but it will be appreciated that the invention could also be used in other applications where it""s desired to take samples of light from an optical device for other control or processing purposes.
Many types of optical devices contain mirrors to manipulate light beams or other light source. In contrast to other common optical elements such as lenses, mirrors generally confine the light to the reflecting side only. This provides a relatively easy access to the light beam with minimal perturbation or interference.
The present invention takes advantage of this fact to sample the reflected light beam for purposes of controlling or improving the functioning of the apparatus, or for other purposes. Examples of other purposes in which it is desirable to provide a sample of the light beam include illumination control, noise reduction, optical tracking, optical alignment, and conditioning of image forming devices. The latter application can include cameras, projectors, scanners, printers, etc. The conditioning can be color or intensely balancing, correction of geometric distortions, etc.
The invention is particularly useful, and is therefore described below, in a large scale display system.
Display systems based on a single image generator are limited in the number of pixels they can display (currently the limit is approximately one million), and in their brightness (the amount of light emitted from a unit image area). In order to exceed these limits, it is necessary to combine several image generators to create a single image, for example, by arranging a plurality of image projectors with their screens arrayed in a side-by-side array to produce a combined display. The quality of the resulting image, however, critically depends on the ability to suppress discontinuities that naturally arise at the boundaries of the individual image generators because of variations, (e.g., in color, light intensity, etc.) in the individual image generators. These variations exist initially among the individual image generators, and also tend to change with time.
In general, light sampling devices create disturbances to the image, or other form of light, emanating from the light source. If the light sampling device is located in a light projector between the light source and the screen, the disturbances are mostly in the form of a shadow; and if the light sampling device is between the viewer and the screen, the disturbance is usually in the form of an obstruction.
If a light sampling devices has to be removed when the image is displayed or the light emanating from the light source is otherwise processed, the light sampling procedure would be considerably complicated, and the cost would be considerably increased.
An object of the present invention is to provide a light sampling device which may be applied to an optical apparatus, such as an image projector, in a relatively convenient manner and at a relatively low cost.
Another object of the invention is to provide such a light sampling device which minimizes the interference with the projected image or other normal use of the light emanating from the light source.
A further object of the invention is to provide an optical apparatus with a light sample device which extracts a required sample of light with a minimum of interference with the normal operation of the optical apparatus.
According to one aspect of the present invention, there is provided optical apparatus, comprising: a source of light; a reflector having a reflecting face on one side facing the source of light to receive light therefrom, the reflecting face having a small interruption therein; and a sampling device located on the opposite side of the reflector aligned with the small interruption therein for extracting a sample of the light received by the reflecting face.
According to one preferred embodiment described below, the small interruption is a small hole through the reflector and reflecting face, and the sampling device is an optical fiber having one end received in the small hole from the opposite side of the reflector.
In another preferred embodiment described below, the small interruption in the reflecting face of the reflector is in the form of a narrow slit therein; and the light sampling device includes a light prism fixed to the opposite side of the reflector.
More particularly, according to further features in this described preferred embodiment, the light prism includes an inlet face parallel to and in contact with the opposite side of the reflector and aligned with the small interruption in the reflecting face, to receive the sample of light therefrom; an inclined face for reflecting the sample of light therefrom; and an outlet face through which the sample of light is transmitted. The light sampling device further includes an optical fiber at the opposite face of the prism, and an optical cube for coupling one end of the optical fiber to the outlet face of the prism. In addition, the optical fiber extends along and parallel to the opposite face of the reflector.
This embodiment of the invention provides a number of advantages. Thus, since the optical fiber extends parallel to the reflector, the light sampling device can be installed very conveniently and compactly on the image projector. In addition, the slit in the reflecting face can be much smaller than the cross-sectional area of the optical fiber, thereby minimizing the interference produced by the light sampling device to the viewed image.
A third preferred embodiment is described wherein the light sampling device includes an optical fiber having an end fixed to the opposite side of the reflector in alignment with the interruption and cut at an angle to make abutting contact with the opposite side of the reflector. In this embodiment, the end of the optical fiber is fixed by an apertured supporting member fixed to the opposite side of the reflector and receiving the optical fiber end.
As indicated earlier, the invention is particularly useful in image projectors and projector systems, in which cases, the source of light would be an image generator.
According to another aspect of the present invention, therefore, there is provided an image projector, comprising: an image generator for generating an image to be projected; a screen for screening the image; and a reflector having a reflecting face facing the image generator for reflecting the image generated thereby onto the screen; the reflecting face of the reflector having a small interruption therein; the opposite side of the reflector, opposite to the reflecting face, including a light sampling device aligned with the small interruption for extracting a sample of light therefrom.
Further features and advantages of the invention will be apparent from the description below.